In general, shape memory alloys show the behavior described below. A permanently deformed alloy at low temperatures recovers its original shape when heated to a temperature above its transformation temperature. Shape memory alloys having this character have been used in many industrial fields, especially pipe coupling and temperature controlling elements. Ni-Ti system shape memory alloys (as in Japanese Laid-Open Patent Publication Sho. 59-150047) are well known as alloys exhibiting excellent mechanical properties, especially high strength and ductility, and thermal stability.
Among the disadvantages of using these alloys are the high cost of the alloying elements and difficulty in their manufacturing process. Other shape memory Cu-base alloys have been developed. For example a Cu-Al-Be system is the subject of the Japanese Laid-Open Patent Publication Sho. 60-75542, Cu-Zn-Al Sytem is the subject of Sho. 60-121246 and a Cu-Ni-Al system is the subject of Sho. 60-187648; but those alloys were found to exhibit mechanical properties and thermal stability of the Cu-base alloys that were inferior to those of a Ni-Ti system. A Cu-26% Zn-4% Al shape memory alloy has exhibited low strength and bad thermal stability while a Cu-14% Al-4% Ni alloy have had low ductility. It is therefore desirable to develop alloys possessing high strength and good ductility as well as excellent thermal stability and low cost.